Beta-amyloid peptide (xcex2A) is a major fibrillar component of neuritic plaques in Alzheimer""s disease (AD) brains and is related to the pathogenesis of the disease. The present invention concerns the discovery of the efficiency of Poly-L-Lysine to dissolve preformed xcex2A fibrils in vitro. Poly-L-Lysine can be used as a universal dissolver of all types of oligomeric xcex2-sheet conformation, precursor of the fibrils, and it may also serve to prevent and/or retard amyloidogenesis in vivo AD and other types of amyloid related disorders.
Alzheimer""s disease (AD) is a progressive neurodegenerative disease of the elderly, characterized by memory loss and dementia. It is the most frequent cause of dementia in the elderly, accounting for more than 15 million cases worldwide. It is pathologically characterized by proteinaceous deposits in various areas of the brain, particularly in the hippocampus and cerebral cortex (1). Such deposits include extracellular amyloid plaques, composed principally of beta-amyloid (xcex2A), and intracellular neurofibrillary tangles comprising tau protein filaments.
The xcex2A, a 4-kDa peptide of 39-43 amino acids, is a metabolic product of a large transmembrane amino acid precursor molecule, the amyloid precursor protein (APP). APP has several isoforms generated by alternative splicing of a pre-mRNA transcribed from a single 19-exon gene located on the long arm of chromosome 21. The major transcripts are APP695, APP751 and APP770 (2,3). Certain cases of inherited AD have been shown to result from mutations in amyloid precursor protein that lead to enhanced cellular production of the amyloidotic xcex2A1-42 peptide which is less soluble and more amyloidogenic than the more common 40-amino acid species. The process of soluble amyloid aggregation into insoluble fibrils is associated with neurotoxicity (4-6), although it is not entirely clear how this is mediated. Furthermore, quantitative histopathology has determined that more than 80% of amyloid plaques are associated with clusters of reactive microglia. As the principal immune effector cells of the brain, activated microglia are capable of releasing cytotoxic agents such as proteolytic enzymes, cytokines, complement proteins, reactive oxygen intermediates, and nitric oxide (7,8). Then, an over-abundance of xcex2A and its accumulation as amyloid fibrils trigger disease pathology. This premise has been strengthened greatly by recent studies showing that mutations in the presenilin proteins, which result in familial early-onset AD (9,10), cause increased production of xcex2A1-42 (11,12). Recently, transgenic mice overexpressing the Lys670-Asn, Met671-Leu double mutation in the APP gene have been shown to have age-related AD-like cognitive changes, amyloid plaques, raised levels of the 40-amino acid form of xcex2-amyloid and even greater elevations of the 42/43 amino acid form of xcex2-amyloid (13). Thus, these experiments not only provide convincing evidence that APP abnormalities can cause AD, but also have established an important resource for the exploration of therapeutic and preventing strategies.
Approaches against amyloid plaques under investigation by several laboratories are by way of identifying compounds that can dissolve preformed xcex2A fibrils (14) and, recently, by way of immunizing with xcex2A (15-17). In this study, we demonstrated that the Poly-L-Lysine is a potent dissolver of preformed xcex2A fibrils in vitro.
The object of the present invention is to identify compounds that can dissolve preformed xcex2A fibrils in vitro. Compounds effective as dissolvers of preformed xcex2A fibrils could serve as potential therapeutic agents in the future for the treatment of AD. For such a purpose, hydrosoluble and biocompatible polymers such as Poly-L-Lysine and Polyethylene glycol were used.